Fuel rails for supplying fuel to fuel injectors of internal combustion engines are well known. A fuel rail is essentially an elongate fuel manifold connected at an inlet end to a fuel supply system and having a plurality of ports for mating with a plurality of fuel injectors to be supplied.
Fuel rail systems may be recirculating, as is commonly employed in diesel engines wherein fuel sedimentation and injector clogging can be a problem. In gasoline-powered engines, fuel rails are more typically “returnless” or dead ended, wherein all fuel supplied to the fuel rail is dispensed by the fuel injectors.
A well-known problem in fuel rail systems, and especially in returnless systems, is pressure pulsations in the fuel itself. It is known that fuel system damping devices are essential to control fuel system acoustical noise and to improve cylinder-to-cylinder fuel distribution.
Various approaches for damping pulsations in fuel delivery systems are known in the prior art.
For a first example, one or more spring diaphragm devices may be attached to the fuel rail or fuel supply line. These provide only point damping and can lose function at low temperatures. They add hardware cost to an engine, complicate the layout of the fuel rail or fuel line, can allow permeation of fuel vapor, and in many cases simply do not provide adequate damping.
For a second example, the fuel rail itself may be configured to have one or more relatively large, thin, flat sidewalls which can flex in response to sharp pressure fluctuations in the supply system, thus damping pressure excursions by absorption. This configuration can provide excellent damping over a limited range of pressure fluctuations but it is not readily enlarged to meet more stringent requirements for pulse suppression. Further, the thin sidewall of the fuel rail can be exposed to outside impact.
For a third example, a fuel rail may be configured to accept an internal damper comprising a sealed pillow having a flat oval cross-section and formed of various materials including thin stainless steel. Air or an inert gas is trapped within the pillow. The wall material is hermetically sealed and impervious to gasoline. Such devices have relatively large, flat or nearly-flat sides that can flex in response to rapid pressure fluctuations in the fuel system. Internal dampers have excellent damping properties, being easily formed to have diaphragm-like walls on both flat sides, and can be used in rails formed of any material provided the rail is large enough to accommodate the damper within.
The damping characteristics of an internal damper are a function of the thickness of the diaphragm wall, the total wall area, and the volume of captive air. To increase the damping capability of a prior art internal damper requires an increase in the captive air volume, a thinner wall, or increased area of the walls.
Reducing wall thickness is not desirable because it reduces the functional margin between stress and yield. Increasing the diaphragm wall area is feasible provided that a) the resulting damper is flexible enough to achieve the desired minimum change in volume for a given change in pressure without approaching the material yield point; b) the resulting damper will withstand cyclic fatigue; and c) the resulting damper is still small enough to fit into the fuel rail. Increasing the size of a fuel rail to accommodate a damper having a larger diameter or longer length is highly undesirable because the space adjacent the engine in a vehicle is already highly congested and limited, and because a new fuel rail design or layout increases the cost of manufacturing an engine.
It is a principal object of the present invention to provide an improved internal fuel rail damper having a greater pulse-damping capability.
It is a further object of the invention to provide such a damper requiring minimal or no change in the size of a fuel rail accepting the damper.
It is a still further object of the invention to provide such a damper having excellent structural stability while still providing excellent wall flexure capability.